[openstack-dev] [horizon] REST and Django
Tripp, Travis S
travis.tripp at hp.com
Fri Dec 12 02:02:30 UTC 2014
Tihomir,
Your comments in the patch were the actually the clearest to me about ease of customizing without requiring upstream changes and really made me think more about your points.
Here are a couple of bullet points for consideration.
* Will we take on auto-discovery of API extensions in two spots (python for legacy and JS for new)?
* As teams move towards deprecating / modifying APIs who will be responsible for ensuring the JS libraries stay up to date and keep tabs on every single project? Right now in Glance, for example, they are working on some fixes to v2 API (soon to become v2.3) that will allow them to deprecate v1 so that Nova can migrate from v1. Part of this includes making simultaneous improvements to the client library so that the switch can happen more transparently to client users. This testing and maintenance of the service team already takes on.
* The service API documentation almost always lags (helped by specs now) and the service team takes on the burden of exposing a programmatic way to access which is tested and easily consumable via the python clients which removes some guesswork from using the service.
* This is going to be an incremental approach with legacy support requirements anyway, I think. So, incorporating python side changes won’t just go away.
* A tangent that needs to be considered IMO since I’m working on some elastic search things right now. Which of these would be better if we introduce a server side caching mechanism or a new source of data such as elastic search to improve performance?
* Would the client just be able to handle changing whether or not it used cache with a header and in either case the server side appropriately uses the cache? (e.g. Cache-Control: no-cache)
I’m not sure I fully understood your example about Cinder. Was it the cinderclient that held up delivery of that horizon support or there cinder API or both? If the API isn’t in, then it would hold up delivery of the feature in any case. If it is just about delivering new functionality, all that would be required in Richard’s approach is to drop in a new file of decorated classes / functions from his utility with the API’s you want? None of the API calls have anything to do with how your view actually replaces the upstream view. These are all just about accessing the data.
Finally, I mentioned the following in the patch related to your example below about the client making two calls to do an update, but wanted to mention here to see if it is an approach that was purposeful (I don’t know the history):
>>Do we really need the lines:
>> project = api.keystone.tenant_get(request, id)
>> kwargs = _tenant_kwargs_from_DATA(request.DATA, enabled=None)
I agree that if you already have all the data it is really bad to have to do another call. I do think there is room for discussing the reasoning, though.
As far as I can tell, they do this so that if you are updating an entity, you have to be very specific about the fields you are changing. I actually see this as potentially a protectionary measure against data loss and a sometimes very nice to have feature. It perhaps was intended to *help* guard against race conditions *sometimes*.
Here's an example: Admin user Joe has an Domain open and stares at it for 15 minutes while he updates the description. Admin user Bob is asked to go ahead and enable it. He opens the record, edits it, and then saves it. Joe finished perfecting the description and saves it. Doing this action would mean that the Domain is enabled and the description gets updated. Last man in still wins if he updates the same fields, but if they update different fields then both of their changes will take affect without them stomping on each other. Whether that is good or bad may depend on the situation…
From: Tihomir Trifonov <t.trifonov at gmail.com<mailto:t.trifonov at gmail.com>>
Reply-To: OpenStack List <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Date: Thursday, December 11, 2014 at 7:53 AM
To: OpenStack List <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Subject: Re: [openstack-dev] [horizon] REST and Django
Client just needs to know which URL to hit in order to invoke a certain API, and does not need to know the procedure name or parameters ordering.
That's where the difference is. I think the client has to know the procedure name and parameters. Otherwise we have a translation factory pattern, that converts one naming convention to another. And you won't be able to call any service API if there is no code in the middleware to translate it to the service API procedure name and parameters. To avoid this - we can use a transparent proxy model - direct mapping of a client call to service API naming, which can be done if the client invokes the methods with the names in the service API, so that the middleware will just pass parameters, and will not translate. Instead of:
updating user data:
<client: POST /user/ > => <middleware: convert to /keystone/update/ > => <keystone: update>
we may use:
<client: POST /keystone/{ver:=x.0}/{method:=update} > => <middleware: just forward to clients[ver].getattr("method")(**kwargs) > => <keystone: update>
The idea here is that if we have keystone 4.0 client, we will have to just add it to the clients [] list and nothing more is required at the middleware level. Just create the frontend code to use the new Keystone 4.0 methods. Otherwise we will have to add all new/different signatures of 4.0 against 2.0/3.0 in the middleware in order to use Keystone 4.0.
There is also a great example of using a pluggable/new feature in Horizon. Do you remember the volume types support patch? The patch was pending in Gerrit for few months - first waiting the cinder support for volume types to go upstream, then waiting few more weeks for review. I am not sure, but as far as I remember, the Horizon patch even missed a release milestone and was introduced in the next release.
If we have a transparent middleware - this will be no more an issue. As long as someone has written the frontend modules(which should be easy to add and customize), and they install the required version of the service API - they will not need updated Horizon to start using the feature. Maybe I am not the right person to give examples here, but how many of you had some kind of Horizon customization being locally merged/patched in your local distros/setups, until the patch is being pushed upstream?
I will say it again. Nova, Keystone, Cinder, Glance etc. already have stable public APIs. Why do we want to add the translation middleware and to introduce another level of REST API? This layer will often hide new features, added to the service APIs and will delay their appearance in Horizon. That's simply not needed. I believe it is possible to just wrap the authentication in the middleware REST, but not to translate anything as RPC methods/parameters.
And one more example:
@rest_utils.ajax()
def put(self, request, id):
"""Update a single project.
The POST data should be an application/json object containing the
parameters to update: "name" (string), "description" (string),
"domain_id" (string) and "enabled" (boolean, defaults to true).
Additional, undefined parameters may also be provided, but you'll have
to look deep into keystone to figure out what they might be.
This method returns HTTP 204 (no content) on success.
"""
project = api.keystone.tenant_get(request, id)
kwargs = _tenant_kwargs_from_DATA(request.DATA, enabled=None)
api.keystone.tenant_update(request, project, **kwargs)
Do we really need the lines:
project = api.keystone.tenant_get(request, id)
kwargs = _tenant_kwargs_from_DATA(request.DATA, enabled=None)
? Since we update the project on the client, it is obvious that we already fetched the project data. So we can simply send:
POST /keystone/3.0/tenant_update
Content-Type: application/json
{"id": cached.id<http://cached.id>, "domain_id": cached.domain_id, "name": "new name", "description": "new description", "enabled": cached.enabled}
Fewer requests, faster application.
On Wed, Dec 10, 2014 at 8:39 PM, Thai Q Tran <tqtran at us.ibm.com<mailto:tqtran at us.ibm.com>> wrote:
I think we're arguing for the same thing, but maybe slightly different approach. I think we can both agree that a middle-layer is required, whether we intend to use it as a proxy or REST endpoints. Regardless of the approach, the client needs to relay what API it wants to invoke, and you can do that either via RPC or REST. I personally prefer the REST approach because it shields the client. Client just needs to know which URL to hit in order to invoke a certain API, and does not need to know the procedure name or parameters ordering. Having said all of that, I do believe we should keep it as thin as possible. I do like the idea of having separate classes for different API versions. What we have today is a thin REST layer that acts like a proxy. You hit a certain URL, and the middle layer forwards the API invokation. The only exception to this rule is support for batch deletions.
-----Tihomir Trifonov <t.trifonov at gmail.com<mailto:t.trifonov at gmail.com>> wrote: -----
To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
From: Tihomir Trifonov <t.trifonov at gmail.com<mailto:t.trifonov at gmail.com>>
Date: 12/10/2014 03:04AM
Subject: Re: [openstack-dev] [horizon] REST and Django
Richard, thanks for the reply,
I agree that the given example is not a real REST. But we already have the REST API - that's Keystone, Nova, Cinder, Glance, Neutron etc, APIs. So what we plan to do here? To add a new REST layer to communicate with other REST API? Do we really need Frontend-REST-REST architecture ? My opinion is that we don't need another REST layer as we currently are trying to go away from the Django layer, which is the same - another processing layer. Although we call it REST proxy or whatever - it doesn't need to be a real REST, but just an aggregation proxy that combines and forwards some requests with adding minimal processing overhead. What makes sense for me is to keep the authentication in this layer as it is now - push a cookie to the frontend, but the REST layer will extract the auth tokens from the session storage and prepare the auth context for the REST API request to OS services. This way we will not expose the tokens to the JS frontend, and will have strict control over the authentication. The frontend will just send data requests, they will be wrapped with auth context and forwarded.
Regarding the existing issues with versions in the API - for me the existing approach is wrong. All these fixes were made as workarounds. What should have been done is to create abstractions for each version and to use a separate class for each version. This was partially done for the keystoneclient in api/keystone.py, but not for the forms/views, where we still have if-else for versions. What I suggest here is to have different(concrete) views/forms for each version, and to use them according the context. If the Keystone backend is v2.0 - then in the Frontend use keystone2() object, otherwise use keystone3() object. This of course needs some more coding, but is much cleaner in terms of customization and testing. For me the current hacks with 'if keystone.version == 3.0' are wrong at many levels. And this can be solved now. The problem till now was that we had one frontend that had to be backed by different versions of backend components. Now we can have different frontends that map to specific backend. That's how I understand the power of Angular with it's views and directives. That's where I see the real benefit of using full-featured frontend. Also imagine how easy will be then to deprecate a component version, compared to what we need to do now for the same.
Otherwise we just rewrite the current Django middleware with another DjangoRest middleware and don't change anything, we don't fix the problems. We just move them to another place.
I still think that in Paris we talked about a new generation of the Dashboard, a different approach on building the frontend for OpenStack. What I've heard there from users/operators of Horizon was that it was extremely hard to add customizations and new features to the Dashboard, as all these needed to go through upstream changes and to wait until next release cycle to get them. Do we still want to address these concerns and how? Please, correct me if I got things wrong.
On Wed, Dec 10, 2014 at 11:56 AM, Richard Jones <r1chardj0n3s at gmail.com<mailto:r1chardj0n3s at gmail.com>> wrote:
Sorry I didn't respond to this earlier today, I had intended to.
What you're describing isn't REST, and the principles of REST are what have been guiding the design of the new API so far. I see a lot of value in using REST approaches, mostly around clarity of the interface.
While the idea of a very thin proxy seemed like a great idea at one point, my conversations at the summit convinced me that there was value in both using the client interfaces present in the openstack_dashboard/api code base (since they abstract away many issues in the apis including across versions) and also value in us being able to clean up (for example, using "project_id" rather than "project" in the user API we've already implemented) and extend those interfaces (to allow batched operations).
We want to be careful about what we expose in Horizon to the JS clients through this API. That necessitates some amount of code in Horizon. About half of the current API for keysone represents that control (the other half is docstrings :)
Richard
On Tue Dec 09 2014 at 9:37:47 PM Tihomir Trifonov <t.trifonov at gmail.com<mailto:t.trifonov at gmail.com>> wrote:
Sorry for the late reply, just few thoughts on the matter.
IMO the REST middleware should be as thin as possible. And I mean thin in terms of processing - it should not do pre/post processing of the requests, but just unpack/pack. So here is an example:
instead of making AJAX calls that contain instructions:
POST --json --data {"action": "delete", "data": [ {"name": "item1"}, {"name": "item2"}, {"name": "item3" ]}
I think a better approach is just to pack/unpack batch commands, and leave execution to the frontend/backend and not middleware:
POST --json --data {"
batch
":
[
{
"
action"
: "delete"
,
"payload":
{"name": "item1"}
,
{
"
action"
: "delete"
,
"payload":
{"name": "item
2
"}
,
{
"
action"
: "delete"
,
"payload":
{"name": "item
3
"}
]
}
The idea is that the middleware should not know the actual data. It should ideally just unpack the data:
responses = []
for cmd in
request.POST['batch']:
responses
.append(
getattr(controller, cmd['action']
)(**
cmd['payload']
))
return responses
and the frontend(JS) will just send batches of simple commands, and will receive a list of responses for each command in the batch. The error handling will be done in the frontend(JS) as well.
For the more complex example of 'put()' where we have dependent objects:
project = api.keystone.tenant_get(request, id)
kwargs = self._tenant_kwargs_from_DATA(request.DATA, enabled=None)
api.keystone.tenant_update(request, project, **kwargs)
In practice the project data should be already present in the frontend(assuming that we already loaded it to render the project form/view), so
POST --json --data {"
batch
":
[
{
"
action"
: "tenant_update"
,
"payload":
{"project": js_project_object.id<http://js_project_object.id>, "name": "some name", "prop1": "some prop", "prop2": "other prop, etc."}
]
}
So in general we don't need to recreate the full state on each REST call, if we make the Frontent full-featured application. This way - the frontend will construct the object, will hold the cached value, and will just send the needed requests as single ones or in batches, will receive the response from the API backend, and will render the results. The whole processing logic will be held in the Frontend(JS), while the middleware will just act as proxy(un/packer). This way we will maintain just the logic in the frontend, and will not need to duplicate some logic in the middleware.
On Tue, Dec 2, 2014 at 4:45 PM, Adam Young <ayoung at redhat.com<mailto:ayoung at redhat.com>> wrote:
On 12/02/2014 12:39 AM, Richard Jones wrote:
On Mon Dec 01 2014 at 4:18:42 PM Thai Q Tran <tqtran at us.ibm.com<mailto:tqtran at us.ibm.com>> wrote:
I agree that keeping the API layer thin would be ideal. I should add that having discrete API calls would allow dynamic population of table. However, I will make a case where it might be necessary to add additional APIs. Consider that you want to delete 3 items in a given table.
If you do this on the client side, you would need to perform: n * (1 API request + 1 AJAX request)
If you have some logic on the server side that batch delete actions: n * (1 API request) + 1 AJAX request
Consider the following:
n = 1, client = 2 trips, server = 2 trips
n = 3, client = 6 trips, server = 4 trips
n = 10, client = 20 trips, server = 11 trips
n = 100, client = 200 trips, server 101 trips
As you can see, this does not scale very well.... something to consider...
This is not something Horizon can fix. Horizon can make matters worse, but cannot make things better.
If you want to delete 3 users, Horizon still needs to make 3 distinct calls to Keystone.
To fix this, we need either batch calls or a standard way to do multiples of the same operation.
The unified API effort it the right place to drive this.
Yep, though in the above cases the client is still going to be hanging, waiting for those server-backend calls, with no feedback until it's all done. I would hope that the client-server call overhead is minimal, but I guess that's probably wishful thinking when in the land of random Internet users hitting some provider's Horizon :)
So yeah, having mulled it over myself I agree that it's useful to have batch operations implemented in the POST handler, the most common operation being DELETE.
Maybe one day we could transition to a batch call with user feedback using a websocket connection.
Richard
[cid:994faa67a8e28335_0.0.1.1]Richard Jones ---11/27/2014 05:38:53 PM---On Fri Nov 28 2014 at 5:58:00 AM Tripp, Travis S <travis.tripp at hp.com<mailto:travis.tripp at hp.com>> wrote:
From: Richard Jones <r1chardj0n3s at gmail.com<mailto:r1chardj0n3s at gmail.com>>
To: "Tripp, Travis S" <travis.tripp at hp.com<mailto:travis.tripp at hp.com>>, OpenStack List <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Date: 11/27/2014 05:38 PM
Subject: Re: [openstack-dev] [horizon] REST and Django
________________________________
On Fri Nov 28 2014 at 5:58:00 AM Tripp, Travis S <travis.tripp at hp.com<mailto:travis.tripp at hp.com>> wrote:
Hi Richard,
You are right, we should put this out on the main ML, so copying thread out to there. ML: FYI that this started after some impromptu IRC discussions about a specific patch led into an impromptu google hangout discussion with all the people on the thread below.
Thanks Travis!
As I mentioned in the review[1], Thai and I were mainly discussing the possible performance implications of network hops from client to horizon server and whether or not any aggregation should occur server side. In other words, some views require several APIs to be queried before any data can displayed and it would eliminate some extra network requests from client to server if some of the data was first collected on the server side across service APIs. For example, the launch instance wizard will need to collect data from quite a few APIs before even the first step is displayed (I’ve listed those out in the blueprint [2]).
The flip side to that (as you also pointed out) is that if we keep the API’s fine grained then the wizard will be able to optimize in one place the calls for data as it is needed. For example, the first step may only need half of the API calls. It also could lead to perceived performance increases just due to the wizard making a call for different data independently and displaying it as soon as it can.
Indeed, looking at the current launch wizard code it seems like you wouldn't need to load all that data for the wizard to be displayed, since only some subset of it would be necessary to display any given panel of the wizard.
I tend to lean towards your POV and starting with discrete API calls and letting the client optimize calls. If there are performance problems or other reasons then doing data aggregation on the server side could be considered at that point.
I'm glad to hear it. I'm a fan of optimising when necessary, and not beforehand :)
Of course if anybody is able to do some performance testing between the two approaches then that could affect the direction taken.
I would certainly like to see us take some measurements when performance issues pop up. Optimising without solid metrics is bad idea :)
Richard
[1] https://review.openstack.org/#/c/136676/8/openstack_dashboard/api/rest/urls.py
[2] https://blueprints.launchpad.net/horizon/+spec/launch-instance-redesign
-Travis
From: Richard Jones <r1chardj0n3s at gmail.com<mailto:r1chardj0n3s at gmail.com>>
Date: Wednesday, November 26, 2014 at 11:55 PM
To: Travis Tripp <travis.tripp at hp.com<mailto:travis.tripp at hp.com>>, Thai Q Tran/Silicon Valley/IBM <tqtran at us.ibm.com<mailto:tqtran at us.ibm.com>>, David Lyle <dklyle0 at gmail.com<mailto:dklyle0 at gmail.com>>, Maxime Vidori <maxime.vidori at enovance.com<mailto:maxime.vidori at enovance.com>>, "Wroblewski, Szymon" <szymon.wroblewski at intel.com<mailto:szymon.wroblewski at intel.com>>, "Wood, Matthew David (HP Cloud - Horizon)" <matt.wood at hp.com<mailto:matt.wood at hp.com>>, "Chen, Shaoquan" <sean.chen2 at hp.com<mailto:sean.chen2 at hp.com>>, "Farina, Matt (HP Cloud)" <matthew.farina at hp.com<mailto:matthew.farina at hp.com>>, Cindy Lu/Silicon Valley/IBM <clu at us.ibm.com<mailto:clu at us.ibm.com>>, Justin Pomeroy/Rochester/IBM <jpomero at us.ibm.com<mailto:jpomero at us.ibm.com>>, Neill Cox <neill.cox at ingenious.com.au<mailto:neill.cox at ingenious.com.au>>
Subject: Re: REST and Django
I'm not sure whether this is the appropriate place to discuss this, or whether I should be posting to the list under [Horizon] but I think we need to have a clear idea of what goes in the REST API and what goes in the client (angular) code.
In my mind, the thinner the REST API the better. Indeed if we can get away with proxying requests through without touching any *client code, that would be great.
Coding additional logic into the REST API means that a developer would need to look in two places, instead of one, to determine what was happening for a particular call. If we keep it thin then the API presented to the client developer is very, very similar to the API presented by the services. Minimum surprise.
Your thoughts?
Richard
On Wed Nov 26 2014 at 2:40:52 PM Richard Jones <r1chardj0n3s at gmail.com<mailto:r1chardj0n3s at gmail.com>> wrote:
Thanks for the great summary, Travis.
I've completed the work I pledged this morning, so now the REST API change set has:
- no rest framework dependency
- AJAX scaffolding in openstack_dashboard.api.rest.utils
- code in openstack_dashboard/api/rest/
- renamed the API from "identity" to "keystone" to be consistent
- added a sample of testing, mostly for my own sanity to check things were working
https://review.openstack.org/#/c/136676
Richard
On Wed Nov 26 2014 at 12:18:25 PM Tripp, Travis S <travis.tripp at hp.com<mailto:travis.tripp at hp.com>> wrote:
Hello all,
Great discussion on the REST urls today! I think that we are on track to come to a common REST API usage pattern. To provide quick summary:
We all agreed that going to a straight REST pattern rather than through tables was a good idea. We discussed using direct get / post in Django views like what Max originally used[1][2] and Thai also started[3] with the identity table rework or to go with djangorestframework [5] like what Richard was prototyping with[4].
The main things we would use from Django Rest Framework were built in JSON serialization (avoid boilerplate), better exception handling, and some request wrapping. However, we all weren’t sure about the need for a full new framework just for that. At the end of the conversation, we decided that it was a cleaner approach, but Richard would see if he could provide some utility code to do that much for us without requiring the full framework. David voiced that he doesn’t want us building out a whole framework on our own either.
So, Richard will do some investigation during his day today and get back to us. Whatever the case, we’ll get a patch in horizon for the base dependency (framework or Richard’s utilities) that both Thai’s work and the launch instance work is dependent upon. We’ll build REST style API’s using the same pattern. We will likely put the rest api’s in horizon/openstack_dashboard/api/rest/.
[1] https://review.openstack.org/#/c/133178/1/openstack_dashboard/workflow/keypair.py
[2] https://review.openstack.org/#/c/133178/1/openstack_dashboard/workflow/launch.py
[3] https://review.openstack.org/#/c/133767/8/openstack_dashboard/dashboards/identity/users/views.py
[4] https://review.openstack.org/#/c/136676/4/openstack_dashboard/rest_api/identity.py
[5] http://www.django-rest-framework.org/
Thanks,
Travis_______________________________________________
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